Breast cancer is a serious disease that accounts for approximately 40,000 deaths per year in the United States alone. Unfortunately, there is no simple, easily addressed cause of breast cancer, and until the root causes can be identified and eliminated, the best way to prevent mortality is early detection. In the past 15 years, breast cancer mortality has been reduced significantly, which is in part due to screening with film-screen mammography. Nonetheless, conventional film-screen mammography lacks sensitivity, especially for certain subgroups of women such as those with dense breast tissue. Digital mammography has shown promise in imaging dense breast tissue, but has otherwise shown only modest clinical effectiveness over film screen mammography. By improving visualization of breast tissue, X-ray computed tomography (CT) of the breast could potentially provide improvements in diagnostic accuracy over conventional mammography. Unfortunately, however, current breast CT prototype systems use "integrating" detectors, which result in sub- optimal spatial resolution and reduced lesion contrast. Since such detectors have no means to distinguish between direct and scattered radiation, overall signal-to-noise ratio (SNR) in the image is also degraded, which further reduces detectability of subtle changes in the tissue density and presence of microcalcifications. To address these issues we propose to develop a cost-effective high-resolution detector element for use in photon-counting digital X-ray imaging systems. The module will consist of a monolithic sensor of appropriate thickness to absorb X-rays with high efficiency, coupled to our specially designed Digital Pixel Sensor (DPS) readout. Each of these pixels will support a high enough data rate to effectively measure individual source X-rays. Practical considerations such as design modularity will be emphasized. In addition to the sensor head, the detector module will include readout electronics, the necessary data acquisition hardware, and software. For the X-ray energies typically used in mammography and digital radiography, this detector would provide high efficiency, high resolution, and photon counting capability with appropriate levels of energy discrimination. Thus, the modular detector is expected to form an important basic building block for clinically meaningful breast CT instruments in particular and for other medical and non-medical CT systems and radiography scanners in general. PUBLIC HEALTH RELEVANCE: The goal of the proposed research is to develop a very high performance, cost effective, individual photon counting detector for breast CT as well as for other medical CT and digital radiography use. The development of such a detector will significantly improve the resolution and sensitivity with which measurements can be made. In turn, this will allow precise screening, diagnosis and staging, and treatments to curtail the progression of and even cure certain cancers, diseases of the heart and disorders of the circulatory system. Outside medical use, this detector will be extremely important for such applications as X-ray inspections at airports and borders.